The present invention relates generally to devices for processing scrap rubber tire carcasses, and more particularly to such a device in which the scrap tire carcass is reduced to particles.
A satisfactory solution to the problem of disposal of used rubber tires has been quite elusive. The common practice of merely stockpiling the tires with no real plan for ultimate disposal is unsatisfactory because such collections of tires are not only eyesores but can also constitute public health hazards. The many hollows formed within a pile of tire carcasses make attractive homes for rodents and are notorious for collecting and holding rainwater which can result in the generation of a substantial quantity of stagnant water in which mosquitoes breed prolifically.
Burying of used tire carcasses in landfills is not only wasteful of dwindling landfill space but is also not very effective. The peculiar shape of rubber tires and their resilient nature give rise to an interesting but annoying phenomenon in which the tires work their way back up to the surface under the influence of forces generated by freeze/thaw cycles.
Various devices for cutting up or shredding used tire carcasses have been proposed. These have the advantage of reducing the amount of space occupied by the tires, facilitating their permanent burial, and reducing or eliminating the public health problems. Nevertheless, tire carcasses are rather tough articles and a relatively large amount of energy can be expended in shredding one. If the ultimate resting place of the tire carcass is going to be a landfill anyway, there is little incentive to incur the additional expense of machinery, fuel and manpower needed to shred the tires, absent governmental regulation. Such regulation is not likely to be forthcoming until the problem is recognized as being of critical importance, and if forthcoming will add a considerable economic burden.
It would be desirable if the scrap rubber in the tires could be reused in a way having some intrinsic economic value, so that the costs of shredding the tires could be recovered or at least partially offset. Several uses for rubber particles are emerging. These include recycling the rubber particles into rubber pads, loading dock and marine bumpers, floor mats, traffic cones, drainage pipe, etc. Another application receiving increasing attention is a filler for road paving asphalt mixtures. Experimental research has shown that asphalt mix in which a portion of the aggregate has been replaced by used rubber tire particles has several advantageous characteristics which make it desirable for road paving purposes. Roads paved with rubber/asphalt mixtures enjoy a higher than normal coefficient of friction with respect to vehicle tires traveling thereon, thus increasing public safety by reducing the slipperiness of the pavement. Such pavements are also more resilient which makes them less likely to crack under the influence of vehicle load and freeze/thaw cycles. The resulting increase in pavement life is a significant advantage. The rubber/asphalt pavement mixtures which provide the above advantages require a rubber particle which is of fairly regular geometric shape and which can be readily graded by particle size. In all of the above mentioned applications, the particle size and "cleanliness" (freedom from contaminents) of the particles are of critical importance.
Prior known apparatus for shredding tires typically is designed to receive the used tire carcass whole and shred it with knives that "attack" the whole tire and tear and shred it. The result is nonuniform chunks of shredded and distressed rubber having cords, fibers and steel wires extending from the individual pieces. Such a product is unacceptable for pavement use.
It is desirable that an apparatus be provided which can process tires "whole" in the sense that the tire in its discarded state can be introduced into the apparatus without preliminary treatment and yet be reduced to particles of relatively uniform size and regular shape. It is further desirable that the resulting particles be to a large degree free from entrained polyester and steel contaminants so that the rubber can be readily separated from the contaminants by conventional separator means which operate on the principles of differential density or magnetic sorting. The present invention provides these features.